Electronic device and thermal type flow meter on vehicle

ABSTRACT

An airtight configuration for keeping down the permeation of corrosive gas from silicone adhesive, and for preventing corrosive gas from entering the case.  
     An electronic device mounted on vehicle. the electronic device has at least one of a portion connecting components, and a portion sealing the clearance or hole where exists in the electronic device.  
     The at least one of the connection portion and the seal portion is constituted by using adhesive or sealant which has at least one of a function adsorbing corrosive gas and a function trapping corrosive gas with chemical reaction.  
     A car-mounted electronic device characterized by reduced permeation of corrosive gas into a case and high reliability.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an electronic device mounted ona vehicle. Such as an electronic device, there are various sensors and acontrol unit installed in an engine room. More particularly, the presentinvention is relates to the configuration of sealing various sensors andto the configuration of sealing the control unit. Various sensors havesensing elements for detecting various physical quantities andelectrical circuits for controlling the sensing elements, and outputvarious quantities as electrical signals. The control unit has amicroprocessor that controls various states of a vehicle in response toelectrical signals of the sensors.

[0003] 2. Prior Art

[0004] An example of the sealing configuration of the above-mentionedtype is found in the thermal type flow meter disclosed in JapaneseApplication Patent Laid-Open Publication No. Hei 06-11373. This type ofthe configuration is used in physical quantity detecting apparatus andcontroller in engine room.

[0005] It will be described below using an example of the thermal typeair flow meter in the Japanese Application Patent Laid-Open PublicationNo. Hei 06-11373. These physical quantity sensors are used under thesevere environmental conditions of high temperature, low temperature andhigh humidity. The air flow sensor has members formed by the so calledinsert-molding with resin, wherein the terminal for holding the heatingresistor and thermo sensitive resistor and the base made of aluminumcharacterized by excellent thermal conductivity are inserted in saidmolded member. The drive circuit for receiving electrical signals of theheating resistor and the thermo sensitive resistor and for outputtingthem to the outside control unit is bonded to the base. The drivecircuit is installed in the case made of resin. In this sealingconfiguration, the cover for covering the case is bonded to the uppersurface of the case. Silicone adhesive is mainly used for connectionbetween the drive circuit and the base, and is also used in many casesfor connection between the base and the case. Further, epoxy adhesive orsilicone adhesive is used for connection between the case and cover.

[0006] silicone components which contains antibacterial and mildew-proofin silicone adhesive is disclosed in Japanese Application PatentLaid-Open Publication No. Hei 07-62242, wherein the silicone compositionis mixed with Zeolite containing 0.1 to 15 wt % silver ion.

SUMMARY OF THE INVENTION

[0007] [Problems to be Solved by the Invention]

[0008] According to the prior art, silicone adhesive is used forconnection between the metallic base for fixing the drive circuit andthe case made of resin, and the drive circuit is hermetically sealed.However, the silicone adhesive itself has a physical property ofallowing gas to pass by. So if the drive circuit is configured so thatthe base and the case are bonded by adhesive, then corrosive gas willenter the case through the silicone-sealed portion.

[0009] Many of the electronic devices on vehicle used under severeworking conditions consist of a hybrid IC substrate. The hybrid ICsubstrate is configured in such a way that conductors for electricwiring and resistors are printed or burnt on the surface of such aninorganic substance as alumina and glass ceramic, further, capacitors,diodes and semiconductor integrating circuits are mounted on the surfaceof the inorganic substance. The corrosive gas has reached the case afterpassing through the silicone adhesive. Thereby, the corrosive gas reactschemically to silver or silver alloy forming the conductor, and silversulfate is generated, consequently there is the possibility of theconductive wire being damaged.

[0010] The present invention is to prevent permeation of corrosive gasin bonded and sealed portions where exist in electric device on vehicle.For example the adhesive for connection between a metallic base and aresin-made case is the silicone adhesive that keeps advantage ofexcellent viscous property, excellent balance of mechanical strength andelongation and superb reliability of the silicone adhesive. Further thesilicone adhesive has the function of preventing permeation of corrosivegas such as sulfur gas or sulfur compound gas including sulfurous acidgas, hydrogen sulfide gas that accelerate corrosion especially for adrive circuit of the electronic device. Or the adhesive has the functionof accelerating delay of permeation. Thereby overcoming the problem ofgas permeability as disadvantage of the sealant. Use of this adhesiveprevents corrosive gas from entering the case, thereby preventingcorrosion of the conducting material of a drive circuit and ensuring ahighly reliable electronic device on vehicle.

[0011] [Means for Solving the Problems]

[0012] The above object can be attained by the inventions described asclaims.

[0013] For example, to provide the function that resists permeation ofcorrosive gas without losing the viscoelastic property of siliconeadhesive, activated carbon for adsorbing corrosive gas in addition tothe ordinary silicon dioxide is added as filler to the silicone polymerwhich dimethyl vinyl polysiloxane or methyl vinyl phenyl polysiloxane isused as a base polymer. Especially porous hard charcoal and activatedcarbon made from palm-shell having been burnt at a temperature of 1,000°C. or more are effective activated carbon. The above object also can beattained by compounding a metallic substance as filler which is easy toreact chemically to sulfur-based gas such as Ag, Fe Co, Ni, Cu. Namelysaid metallic substance functions as trap agent. Here, the trap agent isthe substance which reacts chemically to corrosive gas and traps thegenerated chemical compound in resin.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is across sectional view of the configuration of anelectronic device on vehicle showing the characteristics of the presentinvention;

[0015]FIG. 2 is a drawing representing an environment of an electronicdevice on vehicle;

[0016]FIG. 3 is a drawing representing the configuration of a thermaltype flow meter;

[0017]FIG. 4 is a cross sectional view representing the configuration ofa thermal type flow meter;

[0018]FIG. 5 is a drawing representing the configuration of generalsilicone adhesive;

[0019]FIG. 6 is a schematic drawing showing the configuration ofsilicone adhesive according to the present invention;

[0020]FIG. 7 is a schematic drawing representing adsorption of corrosivegas by activated carbon;

[0021]FIG. 8 is a schematic drawing representing the configuration ofsilicone adhesive according to the present invention;

[0022]FIG. 9 is a schematic drawing representing adsorption of corrosivegas by activated carbon;

[0023]FIG. 10 is a schematic drawing representing various shape of agrain in adsorbent or trap agent;

[0024]FIG. 11 is a drawing a ground plan representing airflow meter aselectronic device on vehicle in another embodiment;

[0025]FIG. 12 is a cross sectional view of the configuration of anelectronic device of FIG. 11.

DETAILED DESCRIPTION OF THE INVENTION

[0026] [Description of the Preferred Embodiments]

[0027] The following describes the embodiments of the present inventionto give more specific explanation of the present invention. The presentinvention is not restricted by the description of these embodiments.

[0028] The following describes the configuration of the electronicdevice mounted on vehicle, the operating environment thereof andproblems, with reference to FIG. 1, FIG. 2. The electrical device canbroadly be classified into a sensor and a control unit. The control unitfunctions as fuel controller and ignition coil controller. The varioussensors detect the physical quantities of intake airflow rate, airtemperature, atmospheric pressure and boost pressure etc. The controlunit has a function of receiving signals and controlling combustionstatus in the cylinder. The igniter and coil are for controlling theignition time inside the cylinder. The features common to theconfiguration of the electronic device mounted on vehicle are that thedevice has an electronic drive circuit 1 or an electronic controldevice. A metallic base 2 supports these circuits. The case 3 installingthe electronic device circuit or the electronic control circuit is fixedon the base 2 by bonding 4. Further, the cover 5 for covering theopening of the case 3 is bonded to the upper surface of the case 3. Theelectronic drive circuit 1 or electronic control circuit is constitutedby a hybrid IC substrate. The hybrid IC substrate is configured in sucha way that wires (conductors) 8 of the circuit and resistors are printedand burnt on the surface of a substrate 7 made of such an inorganicsubstance as ceramic, and capacitors, diodes and semiconductor ICcircuit are mounted thereon on the surface. To accelerate heat radiationfrom the hybrid IC substrate 9, the hybrid IC substrate 9 is bonded tothe metallic base 2 by means of silicone adhesive. A metal having highthermal conductivity, especially aluminum, is often used as metallicbase 2 in order to serve as a heat sink. The case 3 incorporating thehybrid IC board 9 and cover 5 protecting the upper surface of case 3 areformed integral with the connector serving as an interface with theoutput signal of the electronic drive circuit 1. Terminals 11 consistingof the conductive member responsible for transmission of electricsignals are fixed into the plastic forming the case 3 by insert-molding.This configuration is often adopted. Here the sensor detects such thephysical quantities as intake air temperature, intake airflow rate,boost pressure etc. The sensor is configured in such a way that asensing element 10 is installed outside or in the opening of the case,and is connected to the electronic drive circuit 1 via terminal 11. Asshown in a sigh 4, the case 3 is bonded to the base 2, and as shown insigh 4, the cover 5 is also bonded 6 to the case 3. In many electronicdevices on vehicle, resins characterized by excellent injection moldingproperties such as polybutylene terephthalate (PBT),polyphenylenesulfide (PPS), nylon 6, nylon 11 and nylon 12 are used asresin members forming the case 3 and cover 5.

[0029] Here, coefficients of linear expansion of the case 3 and the base2 are much different from each other, so viscoelastic elastic adhesivesuch as silicone 12 is often used for adhesion or sealing 4. The case 3and cover 5 are bonded with an epoxy adhesive if they are made of thesame material, and with silicone adhesive 12 if they are made ofdifferent materials in many cases.

[0030] In many of the electronic devices on vehicles discussed above,silicone adhesive 12 is often utilized for bounding between parts orcomponents. However, silicone adhesive 12 has disadvantages,

[0031] depending on the characteristics peculiar to silicone resin. Inthe engine room of the vehicle with an electronic device mountedthereon, burnt gas is blown back from the engine, and unburnt gas isreturned. The adhesive is exposed to such the atmosphere 13 of stagnanthydrocarbon as intake air passage. Inside the engine room, there are alarge number of such products as rubber ducts and hoses containingsulfur.

[0032] Such products are laid out in greater numbers in engineconstituents. The engine internal temperature reaches the level of 100°C. or more in some of the electronic devices. In this case,sulfur-containing gas or Sulfur compound gas 14 gushes out from a groupof products vulcanized with sulfur such as rubber dust and hose 26.These sulfur gases often change in a environment, and, in some cases,there are mixtures of gases with hydrocarbon 13 and others resultingfrom blowing back of combustion and return of unburnt gas as mentionedabove. An electronic device highly resistant to these corrosive gasesmust be manufactured in order to maintain product reliability, for thefollowing reason: In these car-mounted electronic devices (electronicdevices on vehicle), silver or silver alloy is often used to form aconductive wire 8 on the ceramic IC board 7 of many electronic drivecircuits 1. When corrosive gas, especially sulfur gas or sulfur compoundgas, enters the case 3, the wire made of silver or silver alloy servingas a conductive wire 8 may be corroded by vulcanization, and the wire 8of electronic drive circuit 1 may be disconnected, with the result thatthe electronic drive circuit 1 may fail to operate.

[0033] Silicone adhesive 12 often used in a car-mounted electronicdevice has physical properties inherent to silicone resin; namely, ithas a high gas permeability. Many of the industrial high molecularmaterials of poly-bondage have low gas permeability, and can beclassified as gas shields. Polyamide (nylon, etc.) and, saturatedpolyester resin groups (PBT, PET, etc.) have a low gas permeabilitywhich does not raise any problem in practical sense. However, thepolymer of silicone resin is formed by siloxane bondage where silicone(Si) and oxygen (O) are combined in a straight chain. Since siloxanebondage (—Si—O—Si—) has a large intermolecular distance, it has a highdegree of flexibility, a low steric hindrance in molecular rotation andsmall intermolecular force, hence a high degree of gas permeability.Because of these physical properties, the following problem occurs:Corrosive gas 14 passes through the portion 4 adhered and sealed withadhesive 12, even though this is the sealed portion of a car-mountedelectronic device exposed to the environment of corrosive gas, asdescribed above. Corrosive gas 14 then enters the case 3, and theconductive wire 8 made of silver or silver compound formed on thesurface of the electronic drive circuit 1 is corroded by vulcanizationin the final stage.

[0034] Concerning the sealing structure of the electronic device onvehicle of the present invention, silicone adhesive 12 having a high gaspermeability is given the function that corrosive gas is trapped oradsorbed into the silicone resin, whereby the corrosive gas does notallow to enter the case 3. Namely, the sealing structure is provided bythe silicone adhesive with preventing corrosive gas. For example,corrosive gas is trapped by chemical reaction in the silicone adhesive.Thereby the electronic drive circuit 1 is protected against corrosivegas.

[0035] The following describes the configuration of the siliconeadhesive of the present invention.

[0036] There are a great number of car-mounted electric device types,and it is difficult to describe all these types. The following will takeup representative types of electronic device on vehicle, and willdescribe the configuration of some examples of the thermal type flowmeter for measuring intake airflow rate shown in FIG. 3, as well asembodiments of the present invention. First, a brief description of theair flow meter will be given below. FIGS. 3 and 4 are cross sectionalviews showing the configuration of the thermal type flow meter.

[0037] The thermal type flow meter is a sensor for measuring intakeairflow that is rapidly coming into use in the market in recent years.Thermal type air flow meter 17 has a heating resistor 15 and a thermosensitive resistor 16. The heating resistor 15 is so controlled by atemperature control circuit 18 that the heating resistor always has aconstant difference in temperature from the thermo sensitive resistor 16for measuring air temperature. Since the heating resistor 15 isinstalled in the flow of air, the surface of the heating resistor 15becomes heat radiation that radiates heat into the flow of air, namely,a heat transfer surface. The heat removed to airflow due to this heattransfer is converted into electrical signals, whereby airflow rate ismeasured. The overall constitution is designed as follows. The body 19is holding the thermal type flow meter 17 while introducing intake air.The heating resistor 15, the thermo sensitive resistor 16 and an intakeair temperature sensor 21 are arranged on the sub-path 20 where part ofthe total airflow enters. These resistor elements and temperaturecontrol circuit 18 transmit electrical signals via the terminal 11embedded in the case 3. The specific configuration will be describedbelow. The structural base of the thermal type flow meter 17 is providedby the base 2 for radiating self-generated heat of the power device suchas power transistor. The base 2 is often made of the metallic materialhaving high thermal conductivity, and aluminum is much used as thismaterial. The hybrid IC substrate is bonded on the surface of the base 2by silicone adhesive. The hybrid IC substrate is configured in a suchway that conductive wires 8 and resistors are formed by printing on thesurface of a ceramic IC board, further, semiconductors, capacitors anddiodes is mounted thereon. The case 3 and connector are so molded as tobe integrated. The connector is used as an interface for transmittingsensor signals to the outside or supplying the circuit drive power fromthe outside. The case 3 is adhered and sealed portion 4 by siliconeadhesive 12 on the base 2. After the sensor output characteristics andothers have been adjusted under this conditions, silicone gel 22 as aprotective film of the hybrid IC substrate 9 is poured into the case 3.The upper surface of the case 3 is covered by the cover 5. The case 3and the cover 5 are bonded by a silicone adhesive or epoxy adhesive 12,this adhesive 12 becomes seal portion 6.

[0038] As described above, the silicone adhesive 12 used for adheringmany kinds of members has high gas permeability. When used under highlycorrosive conditions, gas will enter the case 3 through the adhered orsealed portion 4. To protect the parts mounted on the hybrid ICsubstrate 9 and conductive wire 8 against corrosion, it is necessary toimprove the silicone adhesive in such a way that corrosive gas isprevented from passing through the silicone adhesive or is trapped oradsorbed by the silicone adhesive. Thereby, it is enable to product theelectronic device on vehicle including a thermal type flow meter 17 andhaving high reliability against corrosion.

[0039] To put it more specifically, the silicone compound such assilicone adhesive 12 is compounded with adsorbent 24 as filler. As shownin FIG. 5, the normal silicone adhesive 12 is a compound formed in sucha manner that dimethyl polysiloxane polymer or methyl phenylpolysiloxane polymer 27 as base polymer is with about 10 to 60 wt %filler 23 as a reinforcing agent, as well as adhesion reinforcing agentand stabilizer. This filler 23 is impalpable powder of silicon dioxide(silica), and is generally used as industrial high molecular filler 23under the trade name of Aerozil and fumed silica. Using impalpablepowder of silica with different shapes, sizes and statuses, manycompanies are improving the characteristics of resin. According to thepresent invention, adsorbent 24 is compounded as an alternative to thesilica filler 23 to be compounded with silicone resin, as shown in FIG.6. Alternatively, silica 23 and adsorbent 24 are used together. Further,there is an effect of preventing the permeation of corrosive gas in anexternal corrosive environment even when silica 23, adsorbent 24 andneutralizer are used in combination, and are compounded with siliconeresin.

[0040] Activated carbon 25 is most effective as the adsorbent 24 usedhere when consideration is given to all factors including costs andcorrosive gas adsorbing effect. Activated carbon 25 is found over anextensive range from high-purity activated carbon containing very fewimpurities burnt at a high temperature of 1000° C. or more to activatedcarbon containing some impurities burnt at a temperature below 1000° C.Activated carbon material is also found in great varieties, for exampleactivated carbon made from a palm-shell, charcoal and fibrous plantgroups of various types. All of them are included in the scope ofactivated carbon 25 according to the present invention. Further,adsorbent 24 in addition to activated carbon 25, photocatalyst such astitanium oxide, metals having self-cleaning property such as zinc oxide,Zeolite and ion exchange resin are also included in the scope.

[0041] Activated carbon 25 is advantageous especially because itprovides specific adsorption of the gas. If the target gas adsorbed isunderstood clearly, the activated carbon 25 having a high degree ofadsorbing effect for the gas is compounded with silicone adhesive 12.For example, the activated carbon 25 having a high degree of adsorbingeffect for sulfurous acid gas (SO₂) shown in FIG. 7, FIG. 9, andactivated carbon having a high degree of adsorbing effect for hydrogensulfide (H₂O) etc. Only the corrosive gas will be trapped if theactivated carbon 25 is compounded with the silicone adhesive, and gases(such as vapor and air that are not corrosive) except the target gas(corrosive gas) are allowed to pass by since they are not adsorbed bythe activated carbon 25. Thereby only sulfurous acid gas in which iscorrosive gas 14 of sulfur type or hydrogen sulfide having a similarmolecular structure is adsorbed. This will provide a sealingconfiguration characterized by a high degree of adsorbing effect andsuperb reliability for corrosive resistance. Activated carbon 25 has aporous surface 28. If sulfurous acid gas comes close to the activatedcarbon 25 having a great number of pores with a similar shape as that ofsulfurous acid gas molecule on the surface thereof, then it is adsorbedby countless minus ions 29 present on the surface of activated carbon25, and is adsorbed into pores on the surface of activated carbon 25having a shape similar to that of sulfurous acid gas. Depending on thetype of activated carbon 25, gas adsorbed into the pores on the surfaceof activated carbon 25 makes a chemical reaction after having beenadsorbed into pores of activated carbon 25, and is converted into adifferent substance or is neutralized. Such an activated carbon 25 hasbeen developed.

[0042] When consideration is given to the interior of the engine room orintake-air temperature system of a car, gases produced therein creates acorrosive environment since they are sulfur based gas 14 such as H₂S,SO₂, SO_(x), CS₂ and S₈, NO_(x) gas 13 such as NO and N₂O, hydrocarbonsuch as HC, and chlorine gas such as Cl₂. These corrosive gases aremixed in a complicated manner to form a composite mixed gas. If theactivated carbon 25 for adsorbing gas components similar to theabove-mentioned corrosive gas components is compounded, wherebycorrosive gas adsorbing efficiency can be improved. A thermal type airflow meter characterized by improved reliability for corrosionresistance can be provided by sealing with silicone adhesive 12compounded with at least two types of activated carbons 25 orneutralizers having different adsorbing effects as fillers 23.

[0043] As a matter of course, silica to be used as filler 23 originallycompounded with the silicone adhesive is also porous, and is anadsorbent in a sense. It is said, however, that silica is not effectivein adsorbing sulfur based corrosive gas 14. It has been verified thatsilica is effective in adsorbing aliphatic hydrocarbon gas or the like,and zeolite is effective in adsorbing aromatic hydrocarbon. Thus, silicaas filler 23 of silicone adhesive is effective in adsorbing gases ofalcohol and solvents, and is preferably used in combination withactivated carbon 25. It is preferred that 5 wt % or more activatedcarbon 25 as filler to be mixed with silicone adhesive 12 is mixed whilemaintaining the function as a silicone adhesive or sealant.

[0044] One of the advantages of compounding activated carbon 25 asfiller 23 is that regeneration is possible. When the adsorption power ofactivated carbon 25 has reached the point of saturation, it will belost, and the filler 23 will have no function at all, as a matter ofcourse. However, activated carbon 25 is capable of discharging adsorbedgas molecules when the temperature has exceeded a certain level or acertain external state has been reached in the saturated state. After ithas discharged the gas molecules, it is refreshed and regains theadsorption power. This property makes it possible to work as anadsorbent for a long time. Activated carbon 25 is effective inmaintaining reliable of such a product as a car that is used for a longtime. Especially n the case of a thermal type air flow meter, gasmolecules discharged by activated carbon 25 are sucked into a cylinderwhere it is burnt, without affecting the atmosphere very much.

[0045]FIG. 8 is another embodiment of the present invention shown inFIG. 6.

[0046] In this embodiment, impalpable powder 30 of at least one of Ag,Fe, Co, Ni, Cu is compounded as filler 23 with silicone resin, inaddition to silica. The impalpable powder functions as the trapsubstance. This method is effectively especially in the case of sulfurbased corrosive acid gas 14. The sulfur based corrosive acid gas 14adsorbed on the surface of a silicone adhesive and in the process ofpermeation produces a direct chemical reaction with silver (or at leastone of Fe, Co, Ni, Cu) impalpable powder 30 compounded in siliconeadhesive to yield silver sulfide. It is turned into sulfide in thesilicone and is trapped. Thus, reliability for corrosion resistance isimproved by the mechanism that ensures that sulfur based corrosive gas14 does not enter the case 3 housing a hybrid IC board 9, according tothe adhesion/sealing configuration of the present embodiment.

[0047] Generally, the compound forming by mixing silver with siliconeresin can be found on the market. However, such a compound is oftenfound to be an antibacterial resin based on the sterilization functionof silver, a biological resin or mildew proof resin. The presentinvention has been made by focusing attention to the fact that silverhas a high degree of reactivity with sulfur based corrosive gas. Thereis no example that Fe, Co, Ni or Cu has been compounded with siliconeresin as a trap substance.

[0048] If impalpable powder 30 of at least one of silver (Ag), Fe, Co,Ni, Cu compounded in silicone adhesive has a large size, there may be achange in the electric characteristics such as electrical insulation andconductivity that are intrinsic to silicone adhesive. For this reason,the diameter of silver is preferably 10 μm or smaller. When the shape issphere, there is no problem. Concerning the shape of impalpable powder30 or adsorbent 24, as shown in FIG. 10, in addition to sphere,amorphous bulk, flake, needle or unsteady bulk is also effective becauseit ensures a larger surface area. These purities are also important. AsAg, Fe, Co, Ni, or Cu purity is higher, the surface of impalpable powderis more activated and chemical reaction with corrosive gas becomes moreactive. However, for example when silver is alloyed with other metals,especially platinum group metals such as platinum, palladium andiridium, susceptibility to corrosive acid gas will be damaged, wherebychemical reaction for forming a sulfide will be damaged. This is thesame as the alloys of other transition metals such as copper and gold.Therefore, silver purity is preferred to be at least 80 wt %.

[0049] In recent years, impalpable powder with resin coordinated on thesurface of silver, hydrosilyl apatite silver and impalpable powder ofsilver with active base formed on the surface are also effective.

[0050] As described above, adsorbent 24 and/or impalpable powder 30 (atleast one of Ag, Fe, Co, Ni, Cu) are compounded with silicone adhesive,and corrosive gas is adsorbed and/or trapped in the silicone adhesive,thereby preventing permeation into the case. By contrast, anotherembodiment is configured in such a way that adsorbent 24 as a majorpoint of the present invention and impalpable powder 30 of silver (or atleast one of Fe, Co, Ni, Cu) are compounded with the protective film forprotecting the hybrid IC substrate 9 installed in the case 3. Siliconegel 22 is used as the protective film for covering the hybrid ICsubstrate 9 of many electronic devices on vehicle. Silicone gel 22 andsilicone adhesive 12 have basically the same configuration as that forforming the main chain of polymer by the aforementioned siloxanebondage, and the difference is found only in the number of cross linkingpoints, in many cases. Therefore, even if adsorbent 24 and impalpablepowder 30 of silver are compounded with silicone gel 22, it can be usedwithout any problem. Adsorbent 24 and impalpable powder 30 of silver (orat least one of Fe, Co, Ni, Cu) have already been described, and willnot be described here to avoid duplication. A combination of adsorbent24 compounted with silicone adhesive 12, filler of silver impalpablepowder 30, and adsorbent 24 filler compounded with silicone gel 22provides adhesion and sealing configuration characterized by a highreliability for corrosion resistance.

[0051] Further, the adsorbent 24 filler is expected to provide the sameeffect even when compounded with the resin forming the case member andcover member, thereby providing a car-mounted electronic devicecharacterized by high reliability for corrosion resistance.

[0052] The other embodiment is shown as the airflow sensor in FIG. 11and FIG. 12.

[0053] In these Figs, the same sign as sign of above-mentionedembodiment shows the same or a common element. In this embodiment, thespace surrounded by the terminals, the base 2 and the cover 5 formingsub path 20 is filled up with the sealing substance 12 in which has thesame composition as above-mentioned adhesive 12 or sealing material.

[0054] [Effects of the Invention]

[0055] The present invention provides an electronic device on vehiclecharacterized by a high reliability for corrosion resistance to protectthe hybrid IC board mounted in the case against corrosion due tocorrosive acid gas such as corrosive sulfur based compound gas, sulfurgas and nitrogen oxide gas, and alkali gas.

What is claimed is:
 1. An electronic device mounted on vehicle, whereinsaid electronic device has at least one of a portion connectingcomponents, and a portion sealing the clearance or hole where exists inthe electronic device, the at least one of the connection portion andthe seal portion is constituted by using adhesive or sealant which hasat least one of a function adsorbing corrosive gas and a functiontrapping corrosive gas with chemical reaction.
 2. An electronic devicemounted on vehicle according to claim 1, wherein said electronic devicehas an electronic component operated by electric power such as anelectronic circuit substrate, a case installing said electroniccomponent, and a cover covering the opening of said case, said adhesiveor sealant with at least one of said adsorbing function and trappingfunction is used for at least one of between said case and cover,between said electronic component and the base fixing said component,and a clearance or a hole formed in said electronics device
 3. Anelectronic device mounted on vehicle according to claim 1, wherein saidelectronic device has an electronic component operated by electric powersuch as an electronic circuit substrate, a case installing saidelectronic component, and a cover covering the opening of said case, aterminal for connecting to a external device are fixed in at least oneof said case and cover, said adhesive or sealant with at least one ofsaid adsorbing function and trapping function is filled up in at leastone of between said terminal and case, between said terminal and cover,and an exposed portion of said terminal.
 4. An electronic device mountedon vehicle according to claim 1, wherein said adhesive or said sealantcontains at least one of filler having a function of adsorbing corrosivegas such as sulfur gas, sulfur compound gas, nitrogen oxide, COx gas orchlorine gas, and filler having a function of trapping the samecorrosive gas as above.
 5. An electronic device mounted on vehicleaccording to claim 1, wherein the at least one of said connectionportion and seal portion is constituted by a composition indicatedbelow, silicone adhesive or sealant which the base polymer is dimethylvinyl polysiloxane or methyl vinyl phenyl polysiloxane and contains atleast one of filler having a function of adsorbing corrosive gas such assulfur gas, sulfur compound gas, nitrogen oxide, COx gas or chlorinegas, and filler having a function of trapping the same corrosive gas asabove, or, epoxy adhesive or sealant which the base polymer is bisphenolA or bisphenol F and contains at least one of filler having a functionof adsorbing corrosive gas such as sulfur gas, sulfur compound gas,nitrogen oxide, COx gas or chlorine gas, and filler having a function oftrapping the same corrosive gas as above, or, polyurethane adhesive orsealant which the base polymer is an urethane group and contains atleast one of filler having a function of adsorbing corrosive gas such assulfur gas, sulfur compound gas, nitrogen oxide, COx gas or chlorinegas, and filler having a function of trapping the same corrosive gas asabove.
 6. An electronic device mounted on vehicle according to claim 1,wherein said adhesive or said sealant contains at least one of thesubstance adsorbing corrosive gas and the substance trapping corrosivegas with chemical reaction as filler.
 7. An electronic device mounted onvehicle according to claim 1, wherein said adhesive or said sealantcontains an activated carbon as filler adsorbing corrosive gas.
 8. Anelectronic device mounted on vehicle according to claim 1, wherein saidadhesive or sealant contains at least one of Ag, Fe, Co, Ni, Cu asfiller trapping corrosive gas by chemical reaction.
 9. An electronicdevice mounted on vehicle according to claim 1, wherein said adhesive orsaid sealant contains at least one of Ag, Fe, Co, Ni, Cu having a purityof 80 wt % or more as filler trapping corrosive gas by chemicalreaction.
 10. An electronic device mounted on vehicle according to claim1, wherein said adhesive or said sealant contains a silver alloy asfiller trapping corrosive gas by chemical reaction, and the elementalloyed with silver is a platinum group element such as platinum,palladium and rhodium, as well as a nontransition element such as gold,copper, nickel, iron and chromium.
 11. An electronic device mounted onvehicle according to claim 1, wherein said adhesive or said sealantcontains at least one of Ag, Fe, Co, Ni, Cu as filler trapping corrosivegas by chemical reaction, and these metal substances do not exceed 50 μmin diameter.
 12. An electronic device mounted on vehicle according toclaim 1, wherein said adhesive or said sealant contains at least one ofAg, Fe, Co, Ni, Cu as filler trapping corrosive gas by chemicalreaction, and said adhesive or said sealant is spherical, needle-shapedor flake-shaped, or is formed in an amorphous bulk whose specificsurface area can be easily changed.
 13. An electronic device mounted onvehicle according to claim 1, wherein said adhesive or said sealant isconsisted as following, the base polymer is high polymer, and containsas filler at least one of the activated carbon having a specific of ahigh adsorption efficiency to sulfurous gas (SO₂), the activated carbonhaving a specific of a high efficiency of adsorbing hydrogen sulfide(H₂S). The activated carbon having a specific of a high efficiency ofadsorbing sulfur gas as simple substance: (S2, S3, S4, S6, S8 and Sxring states), the activated carbon having a specific of a highefficiency of adsorbing carbon dioxide disulfide gas (CS₂).
 14. Anelectronic device mounted on vehicle according to claim 1, wherein saidadhesive or said sealant is consisted as following, the base polymer ishigh polymer, and contains as filler at least one of titanium oxide, ionexchange resin, and zeolite.
 15. An electronic device mounted on vehicleaccording to claim 1, wherein said adhesive or said sealant is consistedas following, the base polymer is high polymer, and contains at least 5wt % adsorbent for adsorbing corrosive gas.
 16. An electronic devicemounted on vehicle according to claim 1, wherein said adhesive or saidsealant is consisted as following, the base polymer is high polymer, andcontains at least two types of fillers such as, a silicon dioxide asbase filler and adsorbent for adsorbing corrosive gas, or said silicondioxide and agent for neutralizing corrosive gas, and said fillers arecompounded in a dispersed state.
 17. An electronic device mounted onvehicle according to claim 1, wherein said adhesive or said sealant isconsisted as following, the base polymer is a high polymer, and containsa silicon dioxide (silica) and an adsorbent for adsorbing corrosive gasat least 15 wt % in a total.
 18. A thermal type flow meter for measuringthe flow rate, having a heating resistor, a thermal sensitive resistorand an electric circuit driving these resistors, comprising a basemounting said electric circuit, a case installing said electric circuit,and a cover covering the opening of said case, wherein at least one of aconnection portion between said cover and case, and a connection portionbetween said case and cover is constituted by using adhesive or whichhas at least one of a function adsorbing corrosive gas and a functiontrapping corrosive gas with chemical reaction.
 19. An electronic devicemounted on vehicle, wherein the electronic device has a case forinstalling the electric circuit wires for connecting electrically saidelectric circuit, the filler pored into inside of the case to protectsaid wires, and coating members which is protection film of said wires,the at least one of said filler and coating members contains at leastone of the substance for adsorbing corrosive gas and the substance fortrapping corrosive gas with chemical reaction.
 20. An electronic devicemounted on vehicle according to claim 19, wherein said filler issilicone gel, said substance for adsorbing is activated carbon, and saidsubstance for trapping is at least one of Ag, Fe, Co, Ni, Cu, Silveralloy.
 21. An electronic device mounted on vehicle, wherein saidelectronic device has an electronic component operated by electric powersuch as an electronic circuit substrate, a case installing saidelectronic component and a cover covering the opening of said case, theat least one of said case and said cover contains as filler at least oneof the substance for adsorbing corrosive gas and the substance fortrapping corrosive gas with chemical reaction.
 22. An electronic devicemounted on vehicle according to claim 21, wherein said substance foradsorbing is activated carbon, and said substance for trapping is atleast one of Ag, Fe, Co, Ni, Cu, Silver alloy.
 23. An electronic devicemounted on vehicle according to claim 21, wherein said case and coverare saturated polyester such as polybutylene terephthalate etc, orpolyphenylene sulfide used as base polymer, said base polymer containsadsorbent for adsorbing corrosive gas as filler.